Urban agglomeration has become the most salient feature of global urbanization in recent decades, while spatiotemporal patterns and evolution remain poorly understood in urban agglomerations, which ...limit the decision-makers to make more informed decisions to improve the regional environment. Here we selected one of the most rapidly urbanized regions in the world – Pearl River Delta Metropolitan Region (PRDR), located in southern China, as the case. Landsat images spanning from 1995 to 2015 were used to retrieve land surface temperature (LST). Four types of regional heat island (RHI) degree were defined for further analysis. Then multi-scale spatiotemporal patterns and characteristics of RHI were identified with the help of cloud-based computing, spatial and landscape analysis. We found that (1) traditional urban heat island (UHI) appears as an RHI on an urban agglomeration scale. In PRDR, we found RHI expended with increasing connectivity, especially in the estuary areas where isolated UHI gradually merged during the rapid urbanization. (2) The contribution of main cities in PRDR to RHI and the evolutionary trends and pattern, which is changed from a west-east to a southwest-northeast gradient, have been revealed. (3) Considering the scale effect and different RHI categories, we revealed that during the urbanization, the aggregation of the RHI is significant on a larger-scale, and the area of 4 °C ≤ Relative LST ≤ 8 °C is the stable and high-risk area, which provide scientific bases for the governance of the thermal environment on the regional scale. (4) The study also indicates the cooling effect of forests and water is better than that of grassland, while the cooling effect of grassland is uncertain. The methods and results of this study not only have implications on environmental planning and management in the PRDR but also provide useful insights into the thermal environment research and practice in other urban agglomerations.
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•Spatiotemporal patterns and detailed characteristics of RHIs in PRDR was investigated.•Effects and patterns of rapid urbanization on emerging RHIs was revealed.•Hotspots and additional possibilities of heat risk exposure in the PRDR was proposed.•The urgency of thermal environment governance at the regional scale has been proved.•Differences in cooling effect between water, tree and grassland were also discovered.
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•The cooling effect of urban blue-green space and threshold-size-based studies are reviewed.•The controversies and uncertainties on the cooling effect of urban blue-green space are ...revealed.•The basic framework and perspective of the urban cooling effect studies are proposed.•The new technology and method for furthering urban cooling effect studies are suggested.•The implications of the threshold-size of blue-green space for actionable climate adaption planning are discussed.
The cooling effect of blue-green space has been recognized as a promising approach to mitigate the urban heat island (UHI), while the quantitative role (threshold-size for cooling) is still uncertain. This paper aims to present the latest progress and controversies on the studies of the cooling effects of waterbodies, greenspaces, and parks. In order to do this research, international search engines were employed to systematically search peer-reviewed articles, including the cooling effect of blue-green space and threshold-size-based UHI mitigation studies. After that, the inductive analysis is used to analyze the relevant literature. We found that previous studies concentrated on the correlations between different landscape types, temperature variations and the quantification of cooling intensity, etc. However, threshold-size-based research has received less attention, which limits the ability to make specific recommendations for actionable planning and management – usingthe smallest blue-green space for the best cooling effect. The review also revealed the controversies over the effects of blue-green space size, shape, landscape composition and configuration on cooling effect. Besides, we pointed out that the uncertainties (i.e., the optimal proportion of blue-green space in a park) and the reasons of controversial results of the cooling effect need to be further investigated. We also suggested that more attention should be paid to quantify the contributions of local background climate and landscape characteristics to the cooling effect (threshold-size) of blue-green space. This review would give us a deeper understanding of the field and provide insights into actionable climate adaption planning.
•Ecosystem service benefits and losses in the Yangtze River Delta urban agglomeration are calculated.•The patterns and the main providers of ecosystem services within different landscape types are ...revealed.•Multi-scale analyses are used to divide different functional zone areas.•Three functional zones within the Yangtze River Delta urban agglomeration are proposed.
The comprehensive management of ecosystem service benefits and losses provided by landscapes under land-use reorganization is essential for optimizing and regulating landscape patterns and ecological conservation under rapid urbanization. Of the many studies focusing on the quantification and visualization of ecosystem services, few have explored the visualization characteristics of the different scales related to ecosystem services and losses. In this study, we selected one of the most important urban agglomerations in China—the Yangtze River Delta (YRD)—as a case for the analysis of ecosystem service benefits (which include environmental purification, climate and air regulation, and tourism and leisure) and losses (pollen allergies, air pollution, and the heat island effect) and the spatial patterns of both at multiple scales (grid divisions, administrative districts, and functional areas). We found that the value of ecosystem service losses in the YRD, with a net value of approximately −$42.02 × 106, was slightly higher than the value of ecosystem service benefits. The patterns of ecosystem service benefits were consistent with urbanization processes and patterns, with the natural landscape always serving as the main provider of ecosystem service benefits while the spatial pattern of the urbanized landscape determined the ecosystem service losses. Based on K-means clustering using randomly selected objects as an initial cluster center, we divided the YRD into different functional areas (optimized-, key-, and restricted-development zones) within the grid to create divisions with consistent biophysical properties, thereby avoiding the impact of urban administrative boundaries on the results. To facilitate closing the gap between positive and negative ecosystem outcomes in a politically feasible manner, we also identified functional areas in terms of ecosystem service bundles at the administrative district scale. This study obtains quantitative knowledge of functional areas based on ecosystem services benefits and losses, and helps guide sustainable urban agglomeration planning and development.
Considerable specific cross-sectional and review studies have linked exposure to green spaces to improving public health, but there is no bibliometric review attempting to systemically and ...retrospectively analyze these existing articles. Here we aim to uncover global research status, trends, and future prospects in green spaces and health (G-H) research then propose a framework for the underlying mechanisms and pathways that link green space to public health. We obtained 18 961 G-H research publications from the core Web of Science collection from 1901 to 2019, analyzing the characteristics of publication outputs, key scientific disciplines, and differences in performance between countries and institutions. Besides, content analysis was conducted to analyze the keywords, including keyword co-occurrence analysis and keyword clustering analysis. We found: (1) a steady quantitative increase in publications, active journals, and involved countries and institutions since the 1990s; (2) a signi cant increase and changes in G-H related interdisciplinary categories, with environment-related disciplines becoming the mainstream; (3) research focus and trends that were identified based on the analysis of high-frequency co-occurring keywords; (4) three main knowledge domains, namely, green spaces and physical health, mental health, and ecosystem health, that were identified and visualized based on keyword clustering analysis; (5) a framework of underlying mechanisms and pathways linking green space to public health that is proposed based on visualization of the three main knowledge domains. We suggest that the main challenge of G-H research is to further clarify in-depth the underlying mechanisms and pathways from multiple perspectives, including multiple nations, disciplines, and study designs. The lack of co-occurring keywords and clustering information related to social well-being suggests that research related to 'social health' is lacking. Based on a clear understanding of the quantity, quality, and characteristics of green space for public health, a health-based environmental plan should be proposed in the future.
•The benefits of existing natural forest ecosystem on climate mitigation are demonstrated.•RTE is significantly influenced by the specific land conversion processes are found.•RTE dynamic during the ...urbanization might conform to Environmental Kuznets Curve are suggested.•RHI can better describe heat island effect in urban agglomeration context are proposed.
Urbanization has significantly transformed natural surfaces into impervious surfaces, which has subsequently disturbed the balance of the global surface thermal energy. However, key landscape dynamic transfer processes that can affect land surface temperature (LST) and regional thermal environment (RTE) remain poorly understood, especially in the context of urban agglomerations. Hence we selected one of the world's most rapidly urbanized regions – the Pearl-River-Delta Metropolitan Region (PRDR) located in southern China as the case. With the help of Google Cloud Computing, Markov model, and spatial analyses, we have further quantified the strong contributions of urbanization and urban agglomeration development to RTE dynamics and evolution. Specifically, we revealed (1) the cooling effects of ecological land loss and gain are significantly different, which provides evidence that the existing natural ecosystems (especially forests) are valuable for climatic adaptation because newly constructed ecological land does not provide the same cooling effect. (2) We found that the RTE is not only influenced by land cover patterns and process but also significantly dominated by the specific land conversion processes. (3) From 1995 to 2015 in the PRDR, built-up land increased significantly, while the ecological land was significantly reduced, and the isolated urban heat islands were gradually connected and interacted with each other, forming the regional heat island. (4) We also proposed that the relationship between urbanization rate and temperature (RLST) may conform to the Environmental Kuznets Curve. This study enhances the understanding of RTE dynamics and evolution in urban agglomeration and provides important insights into existing natural ecosystem protection and climate adaptation planning.
Utilization of urban green vegetation (UGV) has been recognized as a promising option to mitigate urban heat island (UHI) effect. While we still lack understanding of the contributions of local ...background climate to the cooling effect of UGV. Here we proposed and employed a cooling effect framework and selected eight typical cities located in Temperate Monsoon Climate (TMC) and Mediterranean Climate (MC) demonstrate that local climate condition largely affects the cooling effect of UGV. Specifically, we found increasing (artificial) rainfall and irrigation contribute to improving the cooling intensity of grassland in both climates, particularly in the hot-dry environment. The cities with high relative humidity would restrict the cooling effect of UGV. Increasing wind speed would significantly enhance the tree-covered while weakening the grass-covered UGVs' cooling effect in MC cities. We also identified that, in order to achieve the most effective cooling with the smallest sized tree-covered UGV, the area of trees in both climate zones' cities should generally be planned around 0.5 ha. The method and results enhance understanding of the cooling effect of UGVs on larger (climate) scales and provide important insights for UGV planning and management.
The development of urban accumulations in recent decades has led to the transformation of urban heat islands (UHI) into regional heat islands (RHI). The contributions of the biophysical, climate, and ...socioeconomic factors to RHI in urban agglomeration remain poorly understood. Here Yangtze River Delta urban agglomeration (YRDUA) in eastern China has been selected as a case area to explore the influences trends, of the influencing factors to RHI by using MODIS data from 2003 to 2017. Results showed that, in summer, the area fraction of daytime RHI in YRDUA has increased from 21.74 to 31.03% in 2003 and 2017, respectively. As compared to 2003, the annual nighttime RHI area in 2017 has increased from 7510 to 20,097 km
. The dominant factors of surface RHI intensity (SRHII) showed seasonal variation. Enhanced vegetation index (EVI) (interpretation of 33.27%) was the dominant factor of daytime SRHII in spring. The most important factor was normalized difference build-up density (NDBI) (37.28% and 26.83%, respectively) in summer and autumn. In winter, precipitation (26.16%) was the most influential. At night, Modified Normalized Difference Water Index (MNDWI) had a dominant effect on SRHII in spring (54.12%), autumn (52.62%), and winter (24.19%). The dominant factor of nighttime SRHII in summer was EVI (42%). Moreover, water bodies harm RHI during the day while having a positive effect at night. These findings can provide a theoretical basis for regional environment improvement and regional sustainable development.
Rapid urbanization has caused significant land cover change (LCC) as well as changes in the land surface temperature (LST). However, the crucial land dynamic process, which could significantly ...contribute to the increase in LST and aggravation of the urban heat island (UHI) effect, remains poorly understood. Additionally, a strategy to optimize the most significant decreased land cover type in order to maximize the cooling effect is still lacking. Therefore, in this study, we selected the rapidly urbanizing and ‘hottest’ city in China, Fuzhou, as a case study. Two algorithms were selected to compare and obtain reliable LST data. A land use transfer matrix was used to detect critical contributions leading to the LST variations. The concept of cooling efficiency (CE) and the threshold value of efficiency (TVoE) are also proposed, defined, and calculated. The results show that LST values increased with increasing proportion of built-up land and sharply decreasing proportion of green space. Areas where LST differences exceed 4°C cover 93% of the areas where green spaces decreased. Additionally, the LST variation is not only associated with the dominant land cover types but is also affected by the land cover transfer pattern and dynamics. Finally, we have calculated the TVoE of green space in Fuzhou city to be 4.55±0.5ha. This finding implies that when Fuzhou municipality implements urban/landscape planning, a green space area of 4.55±0.5ha is the most efficient to reduce the heat effect. This study extends the current understanding of LCC dynamics and LST variation. The concepts of the CE and TVoE are meaningful for landscape planning practice and can be used in other cases.
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•SUHI in different time and different global climate zones have significant differences.•The top three most important drivers of SUHI for daytime are PREC, POP, and PRES.•The top ...three most important drivers of SUHI for nighttime are PREC, POP, and AHE.•Natural-anthropogenic drivers interactively affect SUHI in multiple urban grids.•Greening is more effective to mitigate SUHI in arid climate zones when EVI > 0.38.
The inconstant climate change and rapid urbanization substantially disturb the global thermal balance and induce severe urban heat island (UHI) effect, adversely impacting human development and health. Existing literature has revealed the UHI characteristics and driving factors at an urban scale, but interactions between the main factors of a global grid scale assessment on the context of climate zones remain unclear. Therefore, based on the multidimensional climatic and socio-economic statistical datasets, the multi-time scale of surface urban heat island intensity (SUHI) characteristics was investigated in this study to analyze how natural-anthropogenic drivers affect the variance of SUHI and vary in their importance for the changes of other interaction factors. The results show that the mean value of SUHI in summer is higher than in winter, and in daytime is higher than in nighttime on a seasonal and daily scale. SUHIs in different global climate zones have significant differences. When analyzing drivers’ contributions and interactions with LightGBM model and SHAP algorithm, we know that monthly precipitation (PREC), the estimated population (POP) and surface pressure (PRES) are the three major drivers of daytime SUHI. The nighttime SUHI is mainly PREC, POP and anthropogenic heat emission (AHE), the influence rules of the natural driversare mostly opposite to that of daytime. This study highlights the fundamental role of background climate for designing strategies. Irrigation or artificial rainfall will be effective to mitigate SUHI in low rainfall areas, while it is more effective to reduce AHE in high rainfall areas. In where greening can be difficult in the most developed cities, reducing AHE, increasing per capita GDP and controlling the population scale may also contribute to alleviating the SUHI. This study provides ideas for developing responsive urban heat island mitigation policies in a more realistic setting.
The urban heat island (UHI) effect has been recognized as one of the most significant terrestrial surface climate-related consequences of urbanization. However, the traditional definition of the ...urban–rural (UR) division and the newly established local climate zone (LCZ) classification for UHI and urban climate studies do not adequately express the pattern and intensity of UHI. Moreover, these definitions of UHI find it hard to capture the human activity-induced anthropogenic heat that is highly correlated with urban functional zones (UFZ). Therefore, in this study, with a comparison (theory, technology, and application) of the previous definition (UR and LCZ) of UHI and integration of computer programming technology, social sensing, and remote sensing, we develop a new urban functional zone-based urban temperature zoning system (UFZC). The UFZC system is generally a social-based, planning-oriented, and data-driven classification system associated with the urban function and temperature; it can also be effectively used in city management (e.g., urban planning and energy saving). Moreover, in the Beijing case, we tested the UFZC system and preliminarily analyzed the land surface temperature (LST) difference patterns and causes of the 11 UFZC types. We found that, compared to other UFZCs, the PGZ (perseveration green zone)-UFZC has the lowest LST, while the CBZ (center business district zone)-UFZC and GCZ (general commercial zone)-UFZC contribute the most and stable heat sources. This implies that reducing the heat generated by the function of commercial (and industrial) activities is an effective measure to reduce the UHI effect. We also proposed that multi-source temperature datasets with a high spatiotemporal resolution are needed to obtain more accurate results; thus providing more accurate recommendations for mitigating UHI effects. In short, as a new and finer urban temperature zoning system, although UFZC is not intended to supplant the UR and LCZ classifications, it can facilitate more detailed and coupled urban climate studies.
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